I destroyed all the certs on my Enterprise account, and re-did them from scratch.  Now my Enterprise apps are installing normally.  I have no idea why that worked, but it did.   I had to get Apple involved, because somewhere along the line, my app IDs got associated with a "free" developer account somehow, and XCode wouldn't automatically sign my apps with the appropriate account -- only this "free" account, which I don't remember creating.  Apple had to delete the app IDs from that "free" account and then XCode would finally sign them properly, using the proper, paid-for Enterprise account.  It took Apple a couple of days to do that...   Anyway, all I can tell you is that it was definitely a certificate issue.  There is no logical reason for this cert issue to crop up -- the certs didn't expire for a couple of months.  But deleting all my certs, and all my provisioning profiles fixed the problem for me.   Best of luck to you. ... View more